The measurement of current, (and often power, especially for a constant voltage system), by measurement of the magnetic field about a single wire is a well established measurement procedure. Equipment for such measurements are often called clamp-on or snap-on current measurement meters. Such equipment is manufactured by many companies such as Hewlett-Packard, Fluke, Amprobe, Philips, & others. For a.c. measurements, a coil wound around a ferromagnetic core is commonly used as a sensor, (or "pickup device" to detect), the current flow. The ferromagnetic core is then snapped closed, or nearly closed about the single current carrying wire so that the current induces a magnetic field in the ferromagnetic core which acts as a transformer to produce a voltage in the coil wound about the core. The voltage is then amplified or attenuated to give a calibrated meter reading of the current.
A related system is presently manufactured to measure both d.c. and a.c. currents and power. In that system, transformer coupling is generally not utilized. The magnetic field of the current carrying wire is employed to operate upon a hall effect device, and the hall effect device provides a voltage which is proportional to the current in the current carrying wire. The voltage is, once again, amplified or attenuated to provide a meter reading giving the current in the wire, or alternatively, (when the voltage is known), the power carried by the wire. Direct contact methods are utilized to pick up voltages and currents from low intensity sources such as printed circuit traces, the human body, and telephone systems. The present invention would provide a contact-free method of measuring such low intensity sources.
To summarize, commercially available contactless current and power measurement systems utilize the magnetic fields surrounding a single current carrying wire and employ sensors such as solid state hall effect sensors for both a.c. and d.c. current measurements. Alternatively, the sensor employed for a.c. measurements is frequently a coil of wire, (a transformer type of sensor). With either type of sensor, a voltage which is proportional to the current is sensed. The voltage is then amplified or attenuated, (scaled), and metered to provide a reading of the current in the current carrying wire. In most of these measurement systems a ferromagnetic structure is employed to concentrate the local magnetic field. A ferromagnetic structure also tends to shield against the effects of extraneous magnetic fields, and is a useful adjunct to these basic commercial single wire current measuring devices. There are no commercially available non-contact systems which measure the voltages in the wires for single conductors, cables, or printed circuit board traces. There are no commercially available non-contact systems for measuring currents in cables, that is, multiple conductor assemblies bound together, either.